1. Field of the Invention
The present invention relates to a guitar synthesizer. More specifically, the present invention relates to a guitar synthesizer for generating a synthesized sound through synthesization based on a guitar sound signal obtained by a string vibration by touching the strings of a guitar.
2. Description of the Prior Art
With the recent development of the electronic technology, a music synthesizer for generating a sound through synthesization thereof in an electronic manner has been proposed and put into practical use. A well-known example of such music synthesizer is adapted to generate a sound through electronic synthesization based on performance of a keyboard musical instrument comprising a plurality of keys. However, since there are more persons who play a string musical instrument such as a guitar than the number of persons who have been versed in performing a keyboard musical instrument, it is desirable to provide means for generating a sound through synthesization based on a guitar sound signal obtained through performance of a string musical instrument such as a guitar.
Although such an apparatus has been proposed and put on market, such apparatus requires that a sound synthesized in an electronic manner is generated while an inherent feature of a guitar is maintained, in view of the fact that a sound is generated through electronic synthesization based on a guitar sound signal obtained by a string vibration. More specifically, such a synthesizer requires to extract only a fundamental wave component from a guitar sound signal which is obtained by a string vibration and includes harmonics as well as a fundamental wave component.
In extracting a fundamental wave component from a guitar sound signal including harmonics as well as a fundamental wave component obtained from a string vibration of a guitar, for example, conventionally several approaches have been employed, such as a peak holding approach for extracting a fundamental wave component by peak holding a guitar sound signal, a zero cross detecting approach for extracting a fundamental wave component responsive to a guitar sound signal crossing the zero level, and so on.
FIG. 1A shows waveforms for explaining the principle of the operation of the conventional approaches. Consider a case where a fundamental wave component is to be extracted in a rectangle waveform from a guitar sound signal as shown at (A) in FIG. 1A. According to the conventional peak holding approach, the positive and negative peak values of the guitar sound signal are stored and a pulse as shown at (B) in FIG. 1A is generated in synchronism with the peak of the guitar sound signal such that the polarity of the pulse is reversed for each period after one peak value is stored until the following peak value is stored. The approach is based on the thought that peaks appear in association with the fundamental wave component included in the guitar sound signal. On the other hand, according to the zero crossing detection approach, a pulse of a waveform as shown at (C) in FIG. 1A is generated such that the polarity of the pulse is reversed each time when guitar sound signal crosses the zero level. In other words, the approach is based on the thought that the zero crossing occurs in association with the fundamental wave component included in the guitar sound signal.
However, the above described conventional approaches involve a problem because an erroneous detection is liable to occur. More specifically, if and when a guitar sound signal obtained from a string vibration of the strings dominantly comprises a fundamental wave component, the waveform of such guitar sound signal is rather close to the waveform of the fundamental wave component and hence the above described basic thoughts are true and it is possible to extract the fundamental wave component with accuracy. However, if and when such guitar sound signal comprises many harmonic components as well as a fundamental wave component, an erroneous detection of the fundamental wave is liable to occur according to the above described conventional approaches.
FIG. 1B shows waveforms for explaining such malfunction in the extraction of a fundamental wave component according to the above described conventional approaches. Assuming a waveform of a guitar sound signal as shown at (A) in FIG. 1B, which comprises many harmonic components as well as a fundamental wave component, according to the above described peak hold approach, the fundamental wave component is not properly extracted as shown at (B) in FIG. 1B, inasmuch as peaks associated with the fundamental wave component and other peaks not associated with the fundamental wave component are both detected. Similarly, according to the zero crossing detection approach, the zero crossing associated with the fundamental wave component and other zero crossing occurring not in association with the harmonic components are both detected and hence the fundamental wave component is improperly detected as shown at (C) in FIG. 1B. When a guitar sound signal is generated from a string vibration of the strings of such as a guitar, such harmonic components are liable to occur toward the end of an attenuating guitar sound signal rather than at the beginning of a guitar sound signal shortly after the string is touched. Such harmonic components are also liable to occur when a guitar is played using a pick. Accordingly, it is desirable that a guitar synthesizer is provided which is capable of extracting a fundamental wave component with accuracy from a guitar sound signal including harmonics as well as a fundamental wave component throughout the full period of a guitar sound signal obtained from a string vibration caused by touching the strings.